switch-l4t-atf/docs/porting-guide.md

ARM Trusted Firmware Porting Guide

Contents

1. Introduction
2. Common Modifications
   • Common mandatory modifications
   • Handling reset
   • Common mandatory function modifications
   • Common optional modifications
3. Boot Loader stage specific modifications
   • Boot Loader stage 1 (BL1)
   • Boot Loader stage 2 (BL2)
   • FWU Boot Loader stage 2 (BL2U)
   • Boot Loader stage 3-1 (BL31)
   • PSCI implementation (in BL31)
   • Interrupt Management framework (in BL31)
   • Crash Reporting mechanism (in BL31)
4. Build flags
5. C Library
6. Storage abstraction layer

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1. Introduction

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Please note that this document has been updated for the new platform API as required by the PSCI v1.0 implementation. Please refer to the Migration Guide for the previous platform API.

Porting the ARM Trusted Firmware to a new platform involves making some mandatory and optional modifications for both the cold and warm boot paths. Modifications consist of:

• Implementing a platform-specific function or variable,
• Setting up the execution context in a certain way, or
• Defining certain constants (for example #defines).

The platform-specific functions and variables are declared in include/plat/common/platform.h. The firmware provides a default implementation of variables and functions to fulfill the optional requirements. These implementations are all weakly defined; they are provided to ease the porting effort. Each platform port can override them with its own implementation if the default implementation is inadequate.

Platform ports that want to be aligned with standard ARM platforms (for example FVP and Juno) may also use include/plat/arm/common/plat_arm.h and the corresponding source files in plat/arm/common/. These provide standard implementations for some of the required platform porting functions. However, using these functions requires the platform port to implement additional ARM standard platform porting functions. These additional functions are not documented here.

Some modifications are common to all Boot Loader (BL) stages. Section 2 discusses these in detail. The subsequent sections discuss the remaining modifications for each BL stage in detail.

This document should be read in conjunction with the ARM Trusted Firmware User Guide.

2. Common modifications

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This section covers the modifications that should be made by the platform for each BL stage to correctly port the firmware stack. They are categorized as either mandatory or optional.

2.1 Common mandatory modifications

A platform port must enable the Memory Management Unit (MMU) as well as the instruction and data caches for each BL stage. Setting up the translation tables is the responsibility of the platform port because memory maps differ across platforms. A memory translation library (see lib/xlat_tables/) is provided to help in this setup. Note that although this library supports non-identity mappings, this is intended only for re-mapping peripheral physical addresses and allows platforms with high I/O addresses to reduce their virtual address space. All other addresses corresponding to code and data must currently use an identity mapping.

In ARM standard platforms, each BL stage configures the MMU in the platform-specific architecture setup function, blX_plat_arch_setup(), and uses an identity mapping for all addresses.

If the build option USE_COHERENT_MEM is enabled, each platform can allocate a block of identity mapped secure memory with Device-nGnRE attributes aligned to page boundary (4K) for each BL stage. All sections which allocate coherent memory are grouped under coherent_ram. For ex: Bakery locks are placed in a section identified by name bakery_lock inside coherent_ram so that its possible for the firmware to place variables in it using the following C code directive:

__section("bakery_lock")

Or alternatively the following assembler code directive:

.section bakery_lock

The coherent_ram section is a sum of all sections like bakery_lock which are used to allocate any data structures that are accessed both when a CPU is executing with its MMU and caches enabled, and when it's running with its MMU and caches disabled. Examples are given below.

The following variables, functions and constants must be defined by the platform for the firmware to work correctly.

File : platform_def.h [mandatory]

Each platform must ensure that a header file of this name is in the system include path with the following constants defined. This may require updating the list of PLAT_INCLUDES in the platform.mk file. In the ARM development platforms, this file is found in plat/arm/board/<plat_name>/include/.

Platform ports may optionally use the file include/plat/common/common_def.h, which provides typical values for some of the constants below. These values are likely to be suitable for all platform ports.

Platform ports that want to be aligned with standard ARM platforms (for example FVP and Juno) may also use include/plat/arm/common/arm_def.h, which provides standard values for some of the constants below. However, this requires the platform port to define additional platform porting constants in platform_def.h. These additional constants are not documented here.

• #define : PLATFORM_LINKER_FORMAT

  Defines the linker format used by the platform, for example elf64-littleaarch64.

• #define : PLATFORM_LINKER_ARCH

  Defines the processor architecture for the linker by the platform, for example aarch64.

• #define : PLATFORM_STACK_SIZE

  Defines the normal stack memory available to each CPU. This constant is used by plat/common/aarch64/platform_mp_stack.S and plat/common/aarch64/platform_up_stack.S.

• define : CACHE_WRITEBACK_GRANULE

  Defines the size in bits of the largest cache line across all the cache levels in the platform.

• #define : FIRMWARE_WELCOME_STR

  Defines the character string printed by BL1 upon entry into the bl1_main() function.

• #define : PLATFORM_CORE_COUNT

  Defines the total number of CPUs implemented by the platform across all clusters in the system.

• #define : PLAT_NUM_PWR_DOMAINS

  Defines the total number of nodes in the power domain topology tree at all the power domain levels used by the platform. This macro is used by the PSCI implementation to allocate data structures to represent power domain topology.

• #define : PLAT_MAX_PWR_LVL

  Defines the maximum power domain level that the power management operations should apply to. More often, but not always, the power domain level corresponds to affinity level. This macro allows the PSCI implementation to know the highest power domain level that it should consider for power management operations in the system that the platform implements. For example, the Base AEM FVP implements two clusters with a configurable number of CPUs and it reports the maximum power domain level as 1.

• #define : PLAT_MAX_OFF_STATE

  Defines the local power state corresponding to the deepest power down possible at every power domain level in the platform. The local power states for each level may be sparsely allocated between 0 and this value with 0 being reserved for the RUN state. The PSCI implementation uses this value to initialize the local power states of the power domain nodes and to specify the requested power state for a PSCI_CPU_OFF call.

• #define : PLAT_MAX_RET_STATE

  Defines the local power state corresponding to the deepest retention state possible at every power domain level in the platform. This macro should be a value less than PLAT_MAX_OFF_STATE and greater than 0. It is used by the PSCI implementation to distinguish between retention and power down local power states within PSCI_CPU_SUSPEND call.

• #define : PLAT_MAX_PWR_LVL_STATES

  Defines the maximum number of local power states per power domain level that the platform supports. The default value of this macro is 2 since most platforms just support a maximum of two local power states at each power domain level (power-down and retention). If the platform needs to account for more local power states, then it must redefine this macro.

  Currently, this macro is used by the Generic PSCI implementation to size the array used for PSCI_STAT_COUNT/RESIDENCY accounting.

• #define : BL1_RO_BASE

  Defines the base address in secure ROM where BL1 originally lives. Must be aligned on a page-size boundary.

• #define : BL1_RO_LIMIT

  Defines the maximum address in secure ROM that BL1's actual content (i.e. excluding any data section allocated at runtime) can occupy.

• #define : BL1_RW_BASE

  Defines the base address in secure RAM where BL1's read-write data will live at runtime. Must be aligned on a page-size boundary.

• #define : BL1_RW_LIMIT

  Defines the maximum address in secure RAM that BL1's read-write data can occupy at runtime.

• #define : BL2_BASE

  Defines the base address in secure RAM where BL1 loads the BL2 binary image. Must be aligned on a page-size boundary.

• #define : BL2_LIMIT

  Defines the maximum address in secure RAM that the BL2 image can occupy.

• #define : BL31_BASE

  Defines the base address in secure RAM where BL2 loads the BL31 binary image. Must be aligned on a page-size boundary.

• #define : BL31_LIMIT

  Defines the maximum address in secure RAM that the BL31 image can occupy.

For every image, the platform must define individual identifiers that will be used by BL1 or BL2 to load the corresponding image into memory from non-volatile storage. For the sake of performance, integer numbers will be used as identifiers. The platform will use those identifiers to return the relevant information about the image to be loaded (file handler, load address, authentication information, etc.). The following image identifiers are mandatory:

• #define : BL2_IMAGE_ID

  BL2 image identifier, used by BL1 to load BL2.

• #define : BL31_IMAGE_ID

  BL31 image identifier, used by BL2 to load BL31.

• #define : BL33_IMAGE_ID

  BL33 image identifier, used by BL2 to load BL33.

If Trusted Board Boot is enabled, the following certificate identifiers must also be defined:

• #define : TRUSTED_BOOT_FW_CERT_ID

  BL2 content certificate identifier, used by BL1 to load the BL2 content certificate.

• #define : TRUSTED_KEY_CERT_ID

  Trusted key certificate identifier, used by BL2 to load the trusted key certificate.

• #define : SOC_FW_KEY_CERT_ID

  BL31 key certificate identifier, used by BL2 to load the BL31 key certificate.

• #define : SOC_FW_CONTENT_CERT_ID

  BL31 content certificate identifier, used by BL2 to load the BL31 content certificate.

• #define : NON_TRUSTED_FW_KEY_CERT_ID

  BL33 key certificate identifier, used by BL2 to load the BL33 key certificate.

• #define : NON_TRUSTED_FW_CONTENT_CERT_ID

  BL33 content certificate identifier, used by BL2 to load the BL33 content certificate.

• #define : FWU_CERT_ID

  Firmware Update (FWU) certificate identifier, used by NS_BL1U to load the FWU content certificate.

If the AP Firmware Updater Configuration image, BL2U is used, the following must also be defined:

• #define : BL2U_BASE

  Defines the base address in secure memory where BL1 copies the BL2U binary image. Must be aligned on a page-size boundary.

• #define : BL2U_LIMIT

  Defines the maximum address in secure memory that the BL2U image can occupy.

• #define : BL2U_IMAGE_ID

  BL2U image identifier, used by BL1 to fetch an image descriptor corresponding to BL2U.

If the SCP Firmware Update Configuration Image, SCP_BL2U is used, the following must also be defined:

• #define : SCP_BL2U_IMAGE_ID

  SCP_BL2U image identifier, used by BL1 to fetch an image descriptor corresponding to SCP_BL2U. NOTE: TF does not provide source code for this image.

If the Non-Secure Firmware Updater ROM, NS_BL1U is used, the following must also be defined:

• #define : NS_BL1U_BASE

  Defines the base address in non-secure ROM where NS_BL1U executes. Must be aligned on a page-size boundary. NOTE: TF does not provide source code for this image.

• #define : NS_BL1U_IMAGE_ID

  NS_BL1U image identifier, used by BL1 to fetch an image descriptor corresponding to NS_BL1U.

If the Non-Secure Firmware Updater, NS_BL2U is used, the following must also be defined:

• #define : NS_BL2U_BASE

  Defines the base address in non-secure memory where NS_BL2U executes. Must be aligned on a page-size boundary. NOTE: TF does not provide source code for this image.

• #define : NS_BL2U_IMAGE_ID

  NS_BL2U image identifier, used by BL1 to fetch an image descriptor corresponding to NS_BL2U.

If a SCP_BL2 image is supported by the platform, the following constants must also be defined:

• #define : SCP_BL2_IMAGE_ID

  SCP_BL2 image identifier, used by BL2 to load SCP_BL2 into secure memory from platform storage before being transfered to the SCP.

• #define : SCP_FW_KEY_CERT_ID

  SCP_BL2 key certificate identifier, used by BL2 to load the SCP_BL2 key certificate (mandatory when Trusted Board Boot is enabled).

• #define : SCP_FW_CONTENT_CERT_ID

  SCP_BL2 content certificate identifier, used by BL2 to load the SCP_BL2 content certificate (mandatory when Trusted Board Boot is enabled).

If a BL32 image is supported by the platform, the following constants must also be defined:

• #define : BL32_IMAGE_ID

  BL32 image identifier, used by BL2 to load BL32.

• #define : TRUSTED_OS_FW_KEY_CERT_ID

  BL32 key certificate identifier, used by BL2 to load the BL32 key certificate (mandatory when Trusted Board Boot is enabled).

• #define : TRUSTED_OS_FW_CONTENT_CERT_ID

  BL32 content certificate identifier, used by BL2 to load the BL32 content certificate (mandatory when Trusted Board Boot is enabled).

• #define : BL32_BASE

  Defines the base address in secure memory where BL2 loads the BL32 binary image. Must be aligned on a page-size boundary.

• #define : BL32_LIMIT

  Defines the maximum address that the BL32 image can occupy.

If the Test Secure-EL1 Payload (TSP) instantiation of BL32 is supported by the platform, the following constants must also be defined:

• #define : TSP_SEC_MEM_BASE

  Defines the base address of the secure memory used by the TSP image on the platform. This must be at the same address or below BL32_BASE.

• #define : TSP_SEC_MEM_SIZE

  Defines the size of the secure memory used by the BL32 image on the platform. TSP_SEC_MEM_BASE and TSP_SEC_MEM_SIZE must fully accomodate the memory required by the BL32 image, defined by BL32_BASE and BL32_LIMIT.

• #define : TSP_IRQ_SEC_PHY_TIMER

  Defines the ID of the secure physical generic timer interrupt used by the TSP's interrupt handling code.

If the platform port uses the translation table library code, the following constants must also be defined:

• #define : PLAT_XLAT_TABLES_DYNAMIC

  Optional flag that can be set per-image to enable the dynamic allocation of regions even when the MMU is enabled. If not defined, only static functionality will be available, if defined and set to 1 it will also include the dynamic functionality.

• #define : MAX_XLAT_TABLES

  Defines the maximum number of translation tables that are allocated by the translation table library code. To minimize the amount of runtime memory used, choose the smallest value needed to map the required virtual addresses for each BL stage. If PLAT_XLAT_TABLES_DYNAMIC flag is enabled for a BL image, MAX_XLAT_TABLES must be defined to accommodate the dynamic regions as well.

• #define : MAX_MMAP_REGIONS

  Defines the maximum number of regions that are allocated by the translation table library code. A region consists of physical base address, virtual base address, size and attributes (Device/Memory, RO/RW, Secure/Non-Secure), as defined in the mmap_region_t structure. The platform defines the regions that should be mapped. Then, the translation table library will create the corresponding tables and descriptors at runtime. To minimize the amount of runtime memory used, choose the smallest value needed to register the required regions for each BL stage. If PLAT_XLAT_TABLES_DYNAMIC flag is enabled for a BL image, MAX_MMAP_REGIONS must be defined to accommodate the dynamic regions as well.

• #define : ADDR_SPACE_SIZE

  Defines the total size of the address space in bytes. For example, for a 32 bit address space, this value should be (1ull << 32). This definition is now deprecated, platforms should use PLAT_PHY_ADDR_SPACE_SIZE and PLAT_VIRT_ADDR_SPACE_SIZE instead.

• #define : PLAT_VIRT_ADDR_SPACE_SIZE

  Defines the total size of the virtual address space in bytes. For example, for a 32 bit virtual address space, this value should be (1ull << 32).

• #define : PLAT_PHY_ADDR_SPACE_SIZE

  Defines the total size of the physical address space in bytes. For example, for a 32 bit physical address space, this value should be (1ull << 32).

If the platform port uses the IO storage framework, the following constants must also be defined:

• #define : MAX_IO_DEVICES

  Defines the maximum number of registered IO devices. Attempting to register more devices than this value using io_register_device() will fail with -ENOMEM.

• #define : MAX_IO_HANDLES

  Defines the maximum number of open IO handles. Attempting to open more IO entities than this value using io_open() will fail with -ENOMEM.

• #define : MAX_IO_BLOCK_DEVICES

  Defines the maximum number of registered IO block devices. Attempting to register more devices this value using io_dev_open() will fail with -ENOMEM. MAX_IO_BLOCK_DEVICES should be less than MAX_IO_DEVICES. With this macro, multiple block devices could be supported at the same time.

If the platform needs to allocate data within the per-cpu data framework in BL31, it should define the following macro. Currently this is only required if the platform decides not to use the coherent memory section by undefining the USE_COHERENT_MEM build flag. In this case, the framework allocates the required memory within the the per-cpu data to minimize wastage.

• #define : PLAT_PCPU_DATA_SIZE

  Defines the memory (in bytes) to be reserved within the per-cpu data structure for use by the platform layer.

The following constants are optional. They should be defined when the platform memory layout implies some image overlaying like in ARM standard platforms.

• #define : BL31_PROGBITS_LIMIT

  Defines the maximum address in secure RAM that the BL31's progbits sections can occupy.

• #define : TSP_PROGBITS_LIMIT

  Defines the maximum address that the TSP's progbits sections can occupy.

If the platform port uses the PL061 GPIO driver, the following constant may optionally be defined:

• PLAT_PL061_MAX_GPIOS Maximum number of GPIOs required by the platform. This allows control how much memory is allocated for PL061 GPIO controllers. The default value is 32. [For example, define the build flag in platform.mk]: PLAT_PL061_MAX_GPIOS := 160 $(eval $(call add_define,PLAT_PL061_MAX_GPIOS))

If the platform port uses the partition driver, the following constant may optionally be defined:

• PLAT_PARTITION_MAX_ENTRIES Maximum number of partition entries required by the platform. This allows control how much memory is allocated for partition entries. The default value is 128. [For example, define the build flag in platform.mk]: PLAT_PARTITION_MAX_ENTRIES := 12 $(eval $(call add_define,PLAT_PARTITION_MAX_ENTRIES))

File : plat_macros.S [mandatory]

Each platform must ensure a file of this name is in the system include path with the following macro defined. In the ARM development platforms, this file is found in plat/arm/board/<plat_name>/include/plat_macros.S.

• Macro : plat_crash_print_regs

  This macro allows the crash reporting routine to print relevant platform registers in case of an unhandled exception in BL31. This aids in debugging and this macro can be defined to be empty in case register reporting is not desired.

  For instance, GIC or interconnect registers may be helpful for troubleshooting.

2.2 Handling Reset

BL1 by default implements the reset vector where execution starts from a cold or warm boot. BL31 can be optionally set as a reset vector using the RESET_TO_BL31 make variable.

For each CPU, the reset vector code is responsible for the following tasks:

1. Distinguishing between a cold boot and a warm boot.

2. In the case of a cold boot and the CPU being a secondary CPU, ensuring that the CPU is placed in a platform-specific state until the primary CPU performs the necessary steps to remove it from this state.

3. In the case of a warm boot, ensuring that the CPU jumps to a platform- specific address in the BL31 image in the same processor mode as it was when released from reset.

The following functions need to be implemented by the platform port to enable reset vector code to perform the above tasks.

Function : plat_get_my_entrypoint() [mandatory when PROGRAMMABLE_RESET_ADDRESS == 0]

Argument : void
Return   : uintptr_t

This function is called with the MMU and caches disabled (SCTLR_EL3.M = 0 and SCTLR_EL3.C = 0). The function is responsible for distinguishing between a warm and cold reset for the current CPU using platform-specific means. If it's a warm reset, then it returns the warm reset entrypoint point provided to plat_setup_psci_ops() during BL31 initialization. If it's a cold reset then this function must return zero.

This function does not follow the Procedure Call Standard used by the Application Binary Interface for the ARM 64-bit architecture. The caller should not assume that callee saved registers are preserved across a call to this function.

This function fulfills requirement 1 and 3 listed above.

Note that for platforms that support programming the reset address, it is expected that a CPU will start executing code directly at the right address, both on a cold and warm reset. In this case, there is no need to identify the type of reset nor to query the warm reset entrypoint. Therefore, implementing this function is not required on such platforms.

Function : plat_secondary_cold_boot_setup() [mandatory when COLD_BOOT_SINGLE_CPU == 0]

Argument : void

This function is called with the MMU and data caches disabled. It is responsible for placing the executing secondary CPU in a platform-specific state until the primary CPU performs the necessary actions to bring it out of that state and allow entry into the OS. This function must not return.

In the ARM FVP port, when using the normal boot flow, each secondary CPU powers itself off. The primary CPU is responsible for powering up the secondary CPUs when normal world software requires them. When booting an EL3 payload instead, they stay powered on and are put in a holding pen until their mailbox gets populated.

This function fulfills requirement 2 above.

Note that for platforms that can't release secondary CPUs out of reset, only the primary CPU will execute the cold boot code. Therefore, implementing this function is not required on such platforms.

Function : plat_is_my_cpu_primary() [mandatory when COLD_BOOT_SINGLE_CPU == 0]

Argument : void
Return   : unsigned int

This function identifies whether the current CPU is the primary CPU or a secondary CPU. A return value of zero indicates that the CPU is not the primary CPU, while a non-zero return value indicates that the CPU is the primary CPU.

Note that for platforms that can't release secondary CPUs out of reset, only the primary CPU will execute the cold boot code. Therefore, there is no need to distinguish between primary and secondary CPUs and implementing this function is not required.

Function : platform_mem_init() [mandatory]

Argument : void
Return   : void

This function is called before any access to data is made by the firmware, in order to carry out any essential memory initialization.

Function: plat_get_rotpk_info()

Argument : void *, void **, unsigned int *, unsigned int *
Return   : int

This function is mandatory when Trusted Board Boot is enabled. It returns a pointer to the ROTPK stored in the platform (or a hash of it) and its length. The ROTPK must be encoded in DER format according to the following ASN.1 structure:

AlgorithmIdentifier  ::=  SEQUENCE  {
    algorithm         OBJECT IDENTIFIER,
    parameters        ANY DEFINED BY algorithm OPTIONAL
}

SubjectPublicKeyInfo  ::=  SEQUENCE  {
    algorithm         AlgorithmIdentifier,
    subjectPublicKey  BIT STRING
}

In case the function returns a hash of the key:

DigestInfo ::= SEQUENCE {
    digestAlgorithm   AlgorithmIdentifier,
    digest            OCTET STRING
}

The function returns 0 on success. Any other value is treated as error by the Trusted Board Boot. The function also reports extra information related to the ROTPK in the flags parameter:

ROTPK_IS_HASH      : Indicates that the ROTPK returned by the platform is a
                     hash.
ROTPK_NOT_DEPLOYED : This allows the platform to skip certificate ROTPK
                     verification while the platform ROTPK is not deployed.
                     When this flag is set, the function does not need to
                     return a platform ROTPK, and the authentication
                     framework uses the ROTPK in the certificate without
                     verifying it against the platform value. This flag
                     must not be used in a deployed production environment.

Function: plat_get_nv_ctr()

Argument : void *, unsigned int *
Return   : int

This function is mandatory when Trusted Board Boot is enabled. It returns the non-volatile counter value stored in the platform in the second argument. The cookie in the first argument may be used to select the counter in case the platform provides more than one (for example, on platforms that use the default TBBR CoT, the cookie will correspond to the OID values defined in TRUSTED_FW_NVCOUNTER_OID or NON_TRUSTED_FW_NVCOUNTER_OID).

The function returns 0 on success. Any other value means the counter value could not be retrieved from the platform.

Function: plat_set_nv_ctr()

Argument : void *, unsigned int
Return   : int

This function is mandatory when Trusted Board Boot is enabled. It sets a new counter value in the platform. The cookie in the first argument may be used to select the counter (as explained in plat_get_nv_ctr()). The second argument is the updated counter value to be written to the NV counter.

The function returns 0 on success. Any other value means the counter value could not be updated.

Function: plat_set_nv_ctr2()

Argument : void *, const auth_img_desc_t *, unsigned int
Return   : int

This function is optional when Trusted Board Boot is enabled. If this interface is defined, then plat_set_nv_ctr() need not be defined. The first argument passed is a cookie and is typically used to differentiate between a Non Trusted NV Counter and a Trusted NV Counter. The second argument is a pointer to an authentication image descriptor and may be used to decide if the counter is allowed to be updated or not. The third argument is the updated counter value to be written to the NV counter.

The function returns 0 on success. Any other value means the counter value either could not be updated or the authentication image descriptor indicates that it is not allowed to be updated.

2.3 Common mandatory function modifications

The following functions are mandatory functions which need to be implemented by the platform port.

Function : plat_my_core_pos()

Argument : void
Return   : unsigned int

This funtion returns the index of the calling CPU which is used as a CPU-specific linear index into blocks of memory (for example while allocating per-CPU stacks). This function will be invoked very early in the initialization sequence which mandates that this function should be implemented in assembly and should not rely on the avalability of a C runtime environment. This function can clobber x0 - x8 and must preserve x9 - x29.

This function plays a crucial role in the power domain topology framework in PSCI and details of this can be found in Power Domain Topology Design.

Function : plat_core_pos_by_mpidr()

Argument : u_register_t
Return   : int

This function validates the MPIDR of a CPU and converts it to an index, which can be used as a CPU-specific linear index into blocks of memory. In case the MPIDR is invalid, this function returns -1. This function will only be invoked by BL31 after the power domain topology is initialized and can utilize the C runtime environment. For further details about how ARM Trusted Firmware represents the power domain topology and how this relates to the linear CPU index, please refer Power Domain Topology Design.

2.4 Common optional modifications

The following are helper functions implemented by the firmware that perform common platform-specific tasks. A platform may choose to override these definitions.

Function : plat_set_my_stack()

Argument : void
Return   : void

This function sets the current stack pointer to the normal memory stack that has been allocated for the current CPU. For BL images that only require a stack for the primary CPU, the UP version of the function is used. The size of the stack allocated to each CPU is specified by the platform defined constant PLATFORM_STACK_SIZE.

Common implementations of this function for the UP and MP BL images are provided in plat/common/aarch64/platform_up_stack.S and plat/common/aarch64/platform_mp_stack.S

Function : plat_get_my_stack()

Argument : void
Return   : uintptr_t

This function returns the base address of the normal memory stack that has been allocated for the current CPU. For BL images that only require a stack for the primary CPU, the UP version of the function is used. The size of the stack allocated to each CPU is specified by the platform defined constant PLATFORM_STACK_SIZE.

Common implementations of this function for the UP and MP BL images are provided in plat/common/aarch64/platform_up_stack.S and plat/common/aarch64/platform_mp_stack.S

Function : plat_report_exception()

Argument : unsigned int
Return   : void

A platform may need to report various information about its status when an exception is taken, for example the current exception level, the CPU security state (secure/non-secure), the exception type, and so on. This function is called in the following circumstances:

• In BL1, whenever an exception is taken.
• In BL2, whenever an exception is taken.

The default implementation doesn't do anything, to avoid making assumptions about the way the platform displays its status information.

For AArch64, this function receives the exception type as its argument. Possible values for exceptions types are listed in the include/common/bl_common.h header file. Note that these constants are not related to any architectural exception code; they are just an ARM Trusted Firmware convention.

For AArch32, this function receives the exception mode as its argument. Possible values for exception modes are listed in the include/lib/aarch32/arch.h header file.

Function : plat_reset_handler()

Argument : void
Return   : void

A platform may need to do additional initialization after reset. This function allows the platform to do the platform specific intializations. Platform specific errata workarounds could also be implemented here. The api should preserve the values of callee saved registers x19 to x29.

The default implementation doesn't do anything. If a platform needs to override the default implementation, refer to the Firmware Design for general guidelines.

Function : plat_disable_acp()

Argument : void
Return   : void

This api allows a platform to disable the Accelerator Coherency Port (if present) during a cluster power down sequence. The default weak implementation doesn't do anything. Since this api is called during the power down sequence, it has restrictions for stack usage and it can use the registers x0 - x17 as scratch registers. It should preserve the value in x18 register as it is used by the caller to store the return address.

Function : plat_error_handler()

Argument : int
Return   : void

This API is called when the generic code encounters an error situation from which it cannot continue. It allows the platform to perform error reporting or recovery actions (for example, reset the system). This function must not return.

The parameter indicates the type of error using standard codes from errno.h. Possible errors reported by the generic code are:

• -EAUTH: a certificate or image could not be authenticated (when Trusted Board Boot is enabled)
• -ENOENT: the requested image or certificate could not be found or an IO error was detected
• -ENOMEM: resources exhausted. Trusted Firmware does not use dynamic memory, so this error is usually an indication of an incorrect array size

The default implementation simply spins.

Function : plat_panic_handler()

Argument : void
Return   : void

This API is called when the generic code encounters an unexpected error situation from which it cannot recover. This function must not return, and must be implemented in assembly because it may be called before the C environment is initialized.

Note: The address from where it was called is stored in x30 (Link Register). The default implementation simply spins.

Function : plat_get_bl_image_load_info()

Argument : void
Return   : bl_load_info_t *

This function returns pointer to the list of images that the platform has populated to load. This function is currently invoked in BL2 to load the BL3xx images, when LOAD_IMAGE_V2 is enabled.

Function : plat_get_next_bl_params()

Argument : void
Return   : bl_params_t *

This function returns a pointer to the shared memory that the platform has kept aside to pass trusted firmware related information that next BL image needs. This function is currently invoked in BL2 to pass this information to the next BL image, when LOAD_IMAGE_V2 is enabled.

Function : plat_flush_next_bl_params()

Argument : void
Return   : void

This function flushes to main memory all the image params that are passed to next image. This function is currently invoked in BL2 to flush this information to the next BL image, when LOAD_IMAGE_V2 is enabled.

3. Modifications specific to a Boot Loader stage

---

3.1 Boot Loader Stage 1 (BL1)

BL1 implements the reset vector where execution starts from after a cold or warm boot. For each CPU, BL1 is responsible for the following tasks:

1. Handling the reset as described in section 2.2

2. In the case of a cold boot and the CPU being the primary CPU, ensuring that only this CPU executes the remaining BL1 code, including loading and passing control to the BL2 stage.

3. Identifying and starting the Firmware Update process (if required).

4. Loading the BL2 image from non-volatile storage into secure memory at the address specified by the platform defined constant BL2_BASE.

5. Populating a meminfo structure with the following information in memory, accessible by BL2 immediately upon entry.

   meminfo.total_base = Base address of secure RAM visible to BL2
   meminfo.total_size = Size of secure RAM visible to BL2
   meminfo.free_base  = Base address of secure RAM available for
                        allocation to BL2
   meminfo.free_size  = Size of secure RAM available for allocation to BL2
   

   BL1 places this meminfo structure at the beginning of the free memory available for its use. Since BL1 cannot allocate memory dynamically at the moment, its free memory will be available for BL2's use as-is. However, this means that BL2 must read the meminfo structure before it starts using its free memory (this is discussed in Section 3.2).

   In future releases of the ARM Trusted Firmware it will be possible for the platform to decide where it wants to place the meminfo structure for BL2.

   BL1 implements the bl1_init_bl2_mem_layout() function to populate the BL2 meminfo structure. The platform may override this implementation, for example if the platform wants to restrict the amount of memory visible to BL2. Details of how to do this are given below.

The following functions need to be implemented by the platform port to enable BL1 to perform the above tasks.

Function : bl1_early_platform_setup() [mandatory]

Argument : void
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU.

On ARM standard platforms, this function:

• Enables a secure instance of SP805 to act as the Trusted Watchdog.

• Initializes a UART (PL011 console), which enables access to the printf family of functions in BL1.

• Enables issuing of snoop and DVM (Distributed Virtual Memory) requests to the CCI slave interface corresponding to the cluster that includes the primary CPU.

Function : bl1_plat_arch_setup() [mandatory]

Argument : void
Return   : void

This function performs any platform-specific and architectural setup that the platform requires. Platform-specific setup might include configuration of memory controllers and the interconnect.

In ARM standard platforms, this function enables the MMU.

This function helps fulfill requirement 2 above.

Function : bl1_platform_setup() [mandatory]

Argument : void
Return   : void

This function executes with the MMU and data caches enabled. It is responsible for performing any remaining platform-specific setup that can occur after the MMU and data cache have been enabled.

In ARM standard platforms, this function initializes the storage abstraction layer used to load the next bootloader image.

This function helps fulfill requirement 4 above.

Function : bl1_plat_sec_mem_layout() [mandatory]

Argument : void
Return   : meminfo *

This function should only be called on the cold boot path. It executes with the MMU and data caches enabled. The pointer returned by this function must point to a meminfo structure containing the extents and availability of secure RAM for the BL1 stage.

meminfo.total_base = Base address of secure RAM visible to BL1
meminfo.total_size = Size of secure RAM visible to BL1
meminfo.free_base  = Base address of secure RAM available for allocation
                     to BL1
meminfo.free_size  = Size of secure RAM available for allocation to BL1

This information is used by BL1 to load the BL2 image in secure RAM. BL1 also populates a similar structure to tell BL2 the extents of memory available for its own use.

This function helps fulfill requirements 4 and 5 above.

Function : bl1_init_bl2_mem_layout() [optional]

Argument : meminfo *, meminfo *
Return   : void

BL1 needs to tell the next stage the amount of secure RAM available for it to use. This information is populated in a meminfo structure.

Depending upon where BL2 has been loaded in secure RAM (determined by BL2_BASE), BL1 calculates the amount of free memory available for BL2 to use. BL1 also ensures that its data sections resident in secure RAM are not visible to BL2. An illustration of how this is done in ARM standard platforms is given in the Memory layout on ARM development platforms section in the Firmware Design.

Function : bl1_plat_prepare_exit() [optional]

Argument : entry_point_info_t *
Return   : void

This function is called prior to exiting BL1 in response to the BL1_SMC_RUN_IMAGE SMC request raised by BL2. It should be used to perform platform specific clean up or bookkeeping operations before transferring control to the next image. It receives the address of the entry_point_info_t structure passed from BL2. This function runs with MMU disabled.

Function : bl1_plat_set_ep_info() [optional]

Argument : unsigned int image_id, entry_point_info_t *ep_info
Return   : void

This function allows platforms to override ep_info for the given image_id.

The default implementation just returns.

Function : bl1_plat_get_next_image_id() [optional]

Argument : void
Return   : unsigned int

This and the following function must be overridden to enable the FWU feature.

BL1 calls this function after platform setup to identify the next image to be loaded and executed. If the platform returns BL2_IMAGE_ID then BL1 proceeds with the normal boot sequence, which loads and executes BL2. If the platform returns a different image id, BL1 assumes that Firmware Update is required.

The default implementation always returns BL2_IMAGE_ID. The ARM development platforms override this function to detect if firmware update is required, and if so, return the first image in the firmware update process.

Function : bl1_plat_get_image_desc() [optional]

Argument : unsigned int image_id
Return   : image_desc_t *

BL1 calls this function to get the image descriptor information image_desc_t for the provided image_id from the platform.

The default implementation always returns a common BL2 image descriptor. ARM standard platforms return an image descriptor corresponding to BL2 or one of the firmware update images defined in the Trusted Board Boot Requirements specification.

Function : bl1_plat_fwu_done() [optional]

Argument : unsigned int image_id, uintptr_t image_src,
           unsigned int image_size
Return   : void

BL1 calls this function when the FWU process is complete. It must not return. The platform may override this function to take platform specific action, for example to initiate the normal boot flow.

The default implementation spins forever.

Function : bl1_plat_mem_check() [mandatory]

Argument : uintptr_t mem_base, unsigned int mem_size,
           unsigned int flags
Return   : int

BL1 calls this function while handling FWU related SMCs, more specifically when copying or authenticating an image. Its responsibility is to ensure that the region of memory identified by mem_base and mem_size is mapped in BL1, and that this memory corresponds to either a secure or non-secure memory region as indicated by the security state of the flags argument.

This function can safely assume that the value resulting from the addition of mem_base and mem_size fits into a uintptr_t type variable and does not overflow.

This function must return 0 on success, a non-null error code otherwise.

The default implementation of this function asserts therefore platforms must override it when using the FWU feature.

3.2 Boot Loader Stage 2 (BL2)

The BL2 stage is executed only by the primary CPU, which is determined in BL1 using the platform_is_primary_cpu() function. BL1 passed control to BL2 at BL2_BASE. BL2 executes in Secure EL1 and is responsible for:

1. (Optional) Loading the SCP_BL2 binary image (if present) from platform provided non-volatile storage. To load the SCP_BL2 image, BL2 makes use of the meminfo returned by the bl2_plat_get_scp_bl2_meminfo() function. The platform also defines the address in memory where SCP_BL2 is loaded through the optional constant SCP_BL2_BASE. BL2 uses this information to determine if there is enough memory to load the SCP_BL2 image. Subsequent handling of the SCP_BL2 image is platform-specific and is implemented in the bl2_plat_handle_scp_bl2() function. If SCP_BL2_BASE is not defined then this step is not performed.

2. Loading the BL31 binary image into secure RAM from non-volatile storage. To load the BL31 image, BL2 makes use of the meminfo structure passed to it by BL1. This structure allows BL2 to calculate how much secure RAM is available for its use. The platform also defines the address in secure RAM where BL31 is loaded through the constant BL31_BASE. BL2 uses this information to determine if there is enough memory to load the BL31 image.

3. (Optional) Loading the BL32 binary image (if present) from platform provided non-volatile storage. To load the BL32 image, BL2 makes use of the meminfo returned by the bl2_plat_get_bl32_meminfo() function. The platform also defines the address in memory where BL32 is loaded through the optional constant BL32_BASE. BL2 uses this information to determine if there is enough memory to load the BL32 image. If BL32_BASE is not defined then this and the next step is not performed.

4. (Optional) Arranging to pass control to the BL32 image (if present) that has been pre-loaded at BL32_BASE. BL2 populates an entry_point_info structure in memory provided by the platform with information about how BL31 should pass control to the BL32 image.

5. (Optional) Loading the normal world BL33 binary image (if not loaded by other means) into non-secure DRAM from platform storage and arranging for BL31 to pass control to this image. This address is determined using the plat_get_ns_image_entrypoint() function described below.

6. BL2 populates an entry_point_info structure in memory provided by the platform with information about how BL31 should pass control to the other BL images.

The following functions must be implemented by the platform port to enable BL2 to perform the above tasks.

Function : bl2_early_platform_setup() [mandatory]

Argument : meminfo *
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU. The arguments to this function is the address of the meminfo structure populated by BL1.

The platform may copy the contents of the meminfo structure into a private variable as the original memory may be subsequently overwritten by BL2. The copied structure is made available to all BL2 code through the bl2_plat_sec_mem_layout() function.

On ARM standard platforms, this function also:

• Initializes a UART (PL011 console), which enables access to the printf family of functions in BL2.

• Initializes the storage abstraction layer used to load further bootloader images. It is necessary to do this early on platforms with a SCP_BL2 image, since the later bl2_platform_setup must be done after SCP_BL2 is loaded.

Function : bl2_plat_arch_setup() [mandatory]

Argument : void
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU.

The purpose of this function is to perform any architectural initialization that varies across platforms.

On ARM standard platforms, this function enables the MMU.

Function : bl2_platform_setup() [mandatory]

Argument : void
Return   : void

This function may execute with the MMU and data caches enabled if the platform port does the necessary initialization in bl2_plat_arch_setup(). It is only called by the primary CPU.

The purpose of this function is to perform any platform initialization specific to BL2.

In ARM standard platforms, this function performs security setup, including configuration of the TrustZone controller to allow non-secure masters access to most of DRAM. Part of DRAM is reserved for secure world use.

Function : bl2_plat_sec_mem_layout() [mandatory]

Argument : void
Return   : meminfo *

This function should only be called on the cold boot path. It may execute with the MMU and data caches enabled if the platform port does the necessary initialization in bl2_plat_arch_setup(). It is only called by the primary CPU.

The purpose of this function is to return a pointer to a meminfo structure populated with the extents of secure RAM available for BL2 to use. See bl2_early_platform_setup() above.

Following function is required only when LOAD_IMAGE_V2 is enabled.

Function : bl2_plat_handle_post_image_load() [mandatory]

Argument : unsigned int
Return   : int

This function can be used by the platforms to update/use image information for given image_id. This function is currently invoked in BL2 to handle BL image specific information based on the image_id passed, when LOAD_IMAGE_V2 is enabled.

Following functions are required only when LOAD_IMAGE_V2 is disabled.

Function : bl2_plat_get_scp_bl2_meminfo() [mandatory]

Argument : meminfo *
Return   : void

This function is used to get the memory limits where BL2 can load the SCP_BL2 image. The meminfo provided by this is used by load_image() to validate whether the SCP_BL2 image can be loaded within the given memory from the given base.

Function : bl2_plat_handle_scp_bl2() [mandatory]

Argument : image_info *
Return   : int

This function is called after loading SCP_BL2 image and it is used to perform any platform-specific actions required to handle the SCP firmware. Typically it transfers the image into SCP memory using a platform-specific protocol and waits until SCP executes it and signals to the Application Processor (AP) for BL2 execution to continue.

This function returns 0 on success, a negative error code otherwise.

Function : bl2_plat_get_bl31_params() [mandatory]

Argument : void
Return   : bl31_params *

BL2 platform code needs to return a pointer to a bl31_params structure it will use for passing information to BL31. The bl31_params structure carries the following information. - Header describing the version information for interpreting the bl31_param structure - Information about executing the BL33 image in the bl33_ep_info field - Information about executing the BL32 image in the bl32_ep_info field - Information about the type and extents of BL31 image in the bl31_image_info field - Information about the type and extents of BL32 image in the bl32_image_info field - Information about the type and extents of BL33 image in the bl33_image_info field

The memory pointed by this structure and its sub-structures should be accessible from BL31 initialisation code. BL31 might choose to copy the necessary content, or maintain the structures until BL33 is initialised.

Funtion : bl2_plat_get_bl31_ep_info() [mandatory]

Argument : void
Return   : entry_point_info *

BL2 platform code returns a pointer which is used to populate the entry point information for BL31 entry point. The location pointed by it should be accessible from BL1 while processing the synchronous exception to run to BL31.

In ARM standard platforms this is allocated inside a bl2_to_bl31_params_mem structure in BL2 memory.

Function : bl2_plat_set_bl31_ep_info() [mandatory]

Argument : image_info *, entry_point_info *
Return   : void

In the normal boot flow, this function is called after loading BL31 image and it can be used to overwrite the entry point set by loader and also set the security state and SPSR which represents the entry point system state for BL31.

When booting an EL3 payload instead, this function is called after populating its entry point address and can be used for the same purpose for the payload image. It receives a null pointer as its first argument in this case.

Function : bl2_plat_set_bl32_ep_info() [mandatory]

Argument : image_info *, entry_point_info *
Return   : void

This function is called after loading BL32 image and it can be used to overwrite the entry point set by loader and also set the security state and SPSR which represents the entry point system state for BL32.

Function : bl2_plat_set_bl33_ep_info() [mandatory]

Argument : image_info *, entry_point_info *
Return   : void

This function is called after loading BL33 image and it can be used to overwrite the entry point set by loader and also set the security state and SPSR which represents the entry point system state for BL33.

In the preloaded BL33 alternative boot flow, this function is called after populating its entry point address. It is passed a null pointer as its first argument in this case.

Function : bl2_plat_get_bl32_meminfo() [mandatory]

Argument : meminfo *
Return   : void

This function is used to get the memory limits where BL2 can load the BL32 image. The meminfo provided by this is used by load_image() to validate whether the BL32 image can be loaded with in the given memory from the given base.

Function : bl2_plat_get_bl33_meminfo() [mandatory]

Argument : meminfo *
Return   : void

This function is used to get the memory limits where BL2 can load the BL33 image. The meminfo provided by this is used by load_image() to validate whether the BL33 image can be loaded with in the given memory from the given base.

This function isn't needed if either PRELOADED_BL33_BASE or EL3_PAYLOAD_BASE build options are used.

Function : bl2_plat_flush_bl31_params() [mandatory]

Argument : void
Return   : void

Once BL2 has populated all the structures that needs to be read by BL1 and BL31 including the bl31_params structures and its sub-structures, the bl31_ep_info structure and any platform specific data. It flushes all these data to the main memory so that it is available when we jump to later Bootloader stages with MMU off

Function : plat_get_ns_image_entrypoint() [mandatory]

Argument : void
Return   : uintptr_t

As previously described, BL2 is responsible for arranging for control to be passed to a normal world BL image through BL31. This function returns the entrypoint of that image, which BL31 uses to jump to it.

BL2 is responsible for loading the normal world BL33 image (e.g. UEFI).

This function isn't needed if either PRELOADED_BL33_BASE or EL3_PAYLOAD_BASE build options are used.

3.3 FWU Boot Loader Stage 2 (BL2U)

The AP Firmware Updater Configuration, BL2U, is an optional part of the FWU process and is executed only by the primary CPU. BL1 passes control to BL2U at BL2U_BASE. BL2U executes in Secure-EL1 and is responsible for:

1. (Optional) Transfering the optional SCP_BL2U binary image from AP secure memory to SCP RAM. BL2U uses the SCP_BL2U image_info passed by BL1. SCP_BL2U_BASE defines the address in AP secure memory where SCP_BL2U should be copied from. Subsequent handling of the SCP_BL2U image is implemented by the platform specific bl2u_plat_handle_scp_bl2u() function. If SCP_BL2U_BASE is not defined then this step is not performed.

2. Any platform specific setup required to perform the FWU process. For example, ARM standard platforms initialize the TZC controller so that the normal world can access DDR memory.

The following functions must be implemented by the platform port to enable BL2U to perform the tasks mentioned above.

Function : bl2u_early_platform_setup() [mandatory]

Argument : meminfo *mem_info, void *plat_info
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU. The arguments to this function is the address of the meminfo structure and platform specific info provided by BL1.

The platform may copy the contents of the mem_info and plat_info into private storage as the original memory may be subsequently overwritten by BL2U.

On ARM CSS platforms plat_info is interpreted as an image_info_t structure, to extract SCP_BL2U image information, which is then copied into a private variable.

Function : bl2u_plat_arch_setup() [mandatory]

Argument : void
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU.

The purpose of this function is to perform any architectural initialization that varies across platforms, for example enabling the MMU (since the memory map differs across platforms).

Function : bl2u_platform_setup() [mandatory]

Argument : void
Return   : void

This function may execute with the MMU and data caches enabled if the platform port does the necessary initialization in bl2u_plat_arch_setup(). It is only called by the primary CPU.

The purpose of this function is to perform any platform initialization specific to BL2U.

In ARM standard platforms, this function performs security setup, including configuration of the TrustZone controller to allow non-secure masters access to most of DRAM. Part of DRAM is reserved for secure world use.

Function : bl2u_plat_handle_scp_bl2u() [optional]

Argument : void
Return   : int

This function is used to perform any platform-specific actions required to handle the SCP firmware. Typically it transfers the image into SCP memory using a platform-specific protocol and waits until SCP executes it and signals to the Application Processor (AP) for BL2U execution to continue.

This function returns 0 on success, a negative error code otherwise. This function is included if SCP_BL2U_BASE is defined.

3.4 Boot Loader Stage 3-1 (BL31)

During cold boot, the BL31 stage is executed only by the primary CPU. This is determined in BL1 using the platform_is_primary_cpu() function. BL1 passes control to BL31 at BL31_BASE. During warm boot, BL31 is executed by all CPUs. BL31 executes at EL3 and is responsible for:

1. Re-initializing all architectural and platform state. Although BL1 performs some of this initialization, BL31 remains resident in EL3 and must ensure that EL3 architectural and platform state is completely initialized. It should make no assumptions about the system state when it receives control.

2. Passing control to a normal world BL image, pre-loaded at a platform- specific address by BL2. BL31 uses the entry_point_info structure that BL2 populated in memory to do this.

3. Providing runtime firmware services. Currently, BL31 only implements a subset of the Power State Coordination Interface (PSCI) API as a runtime service. See Section 3.3 below for details of porting the PSCI implementation.

4. Optionally passing control to the BL32 image, pre-loaded at a platform- specific address by BL2. BL31 exports a set of apis that allow runtime services to specify the security state in which the next image should be executed and run the corresponding image. BL31 uses the entry_point_info structure populated by BL2 to do this.

If BL31 is a reset vector, It also needs to handle the reset as specified in section 2.2 before the tasks described above.

The following functions must be implemented by the platform port to enable BL31 to perform the above tasks.

Function : bl31_early_platform_setup() [mandatory]

Argument : bl31_params *, void *
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU. The arguments to this function are:

• The address of the bl31_params structure populated by BL2.
• An opaque pointer that the platform may use as needed.

The platform can copy the contents of the bl31_params structure and its sub-structures into private variables if the original memory may be subsequently overwritten by BL31 and similarly the void * pointing to the platform data also needs to be saved.

In ARM standard platforms, BL2 passes a pointer to a bl31_params structure in BL2 memory. BL31 copies the information in this pointer to internal data structures. It also performs the following:

• Initialize a UART (PL011 console), which enables access to the printf family of functions in BL31.

• Enable issuing of snoop and DVM (Distributed Virtual Memory) requests to the CCI slave interface corresponding to the cluster that includes the primary CPU.

Function : bl31_plat_arch_setup() [mandatory]

Argument : void
Return   : void

This function executes with the MMU and data caches disabled. It is only called by the primary CPU.

The purpose of this function is to perform any architectural initialization that varies across platforms.

On ARM standard platforms, this function enables the MMU.

Function : bl31_platform_setup() [mandatory]

Argument : void
Return   : void

This function may execute with the MMU and data caches enabled if the platform port does the necessary initialization in bl31_plat_arch_setup(). It is only called by the primary CPU.

The purpose of this function is to complete platform initialization so that both BL31 runtime services and normal world software can function correctly.

On ARM standard platforms, this function does the following:

• Initialize the generic interrupt controller.

  Depending on the GIC driver selected by the platform, the appropriate GICv2 or GICv3 initialization will be done, which mainly consists of:

  • Enable secure interrupts in the GIC CPU interface.
  • Disable the legacy interrupt bypass mechanism.
  • Configure the priority mask register to allow interrupts of all priorities to be signaled to the CPU interface.
  • Mark SGIs 8-15 and the other secure interrupts on the platform as secure.
  • Target all secure SPIs to CPU0.
  • Enable these secure interrupts in the GIC distributor.
  • Configure all other interrupts as non-secure.
  • Enable signaling of secure interrupts in the GIC distributor.

• Enable system-level implementation of the generic timer counter through the memory mapped interface.

• Grant access to the system counter timer module

• Initialize the power controller device.

  In particular, initialise the locks that prevent concurrent accesses to the power controller device.

Function : bl31_plat_runtime_setup() [optional]

Argument : void
Return   : void

The purpose of this function is allow the platform to perform any BL31 runtime setup just prior to BL31 exit during cold boot. The default weak implementation of this function will invoke console_uninit() which will suppress any BL31 runtime logs.

In ARM Standard platforms, this function will initialize the BL31 runtime console which will cause all further BL31 logs to be output to the runtime console.

Function : bl31_get_next_image_info() [mandatory]

Argument : unsigned int
Return   : entry_point_info *

This function may execute with the MMU and data caches enabled if the platform port does the necessary initializations in bl31_plat_arch_setup().

This function is called by bl31_main() to retrieve information provided by BL2 for the next image in the security state specified by the argument. BL31 uses this information to pass control to that image in the specified security state. This function must return a pointer to the entry_point_info structure (that was copied during bl31_early_platform_setup()) if the image exists. It should return NULL otherwise.

Function : plat_get_syscnt_freq2() [mandatory]

Argument : void
Return   : unsigned int

This function is used by the architecture setup code to retrieve the counter frequency for the CPU's generic timer. This value will be programmed into the CNTFRQ_EL0 register. In ARM standard platforms, it returns the base frequency of the system counter, which is retrieved from the first entry in the frequency modes table.

#define : PLAT_PERCPU_BAKERY_LOCK_SIZE [optional]

When USE_COHERENT_MEM = 0, this constant defines the total memory (in bytes) aligned to the cache line boundary that should be allocated per-cpu to accommodate all the bakery locks.

If this constant is not defined when USE_COHERENT_MEM = 0, the linker calculates the size of the bakery_lock input section, aligns it to the nearest CACHE_WRITEBACK_GRANULE, multiplies it with PLATFORM_CORE_COUNT and stores the result in a linker symbol. This constant prevents a platform from relying on the linker and provide a more efficient mechanism for accessing per-cpu bakery lock information.

If this constant is defined and its value is not equal to the value calculated by the linker then a link time assertion is raised. A compile time assertion is raised if the value of the constant is not aligned to the cache line boundary.

3.5 Power State Coordination Interface (in BL31)

The ARM Trusted Firmware's implementation of the PSCI API is based around the concept of a power domain. A power domain is a CPU or a logical group of CPUs which share some state on which power management operations can be performed as specified by PSCI. Each CPU in the system is assigned a cpu index which is a unique number between 0 and PLATFORM_CORE_COUNT - 1. The power domains are arranged in a hierarchical tree structure and each power domain can be identified in a system by the cpu index of any CPU that is part of that domain and a power domain level. A processing element (for example, a CPU) is at level 0. If the power domain node above a CPU is a logical grouping of CPUs that share some state, then level 1 is that group of CPUs (for example, a cluster), and level 2 is a group of clusters (for example, the system). More details on the power domain topology and its organization can be found in Power Domain Topology Design.

BL31's platform initialization code exports a pointer to the platform-specific power management operations required for the PSCI implementation to function correctly. This information is populated in the plat_psci_ops structure. The PSCI implementation calls members of the plat_psci_ops structure for performing power management operations on the power domains. For example, the target CPU is specified by its MPIDR in a PSCI CPU_ON call. The pwr_domain_on() handler (if present) is called for the CPU power domain.

The power-state parameter of a PSCI CPU_SUSPEND call can be used to describe composite power states specific to a platform. The PSCI implementation defines a generic representation of the power-state parameter viz which is an array of local power states where each index corresponds to a power domain level. Each entry contains the local power state the power domain at that power level could enter. It depends on the validate_power_state() handler to convert the power-state parameter (possibly encoding a composite power state) passed in a PSCI CPU_SUSPEND call to this representation.

The following functions form part of platform port of PSCI functionality.

Function : plat_psci_stat_accounting_start() [optional]

Argument : const psci_power_state_t *
Return   : void

This is an optional hook that platforms can implement for residency statistics accounting before entering a low power state. The pwr_domain_state field of state_info (first argument) can be inspected if stat accounting is done differently at CPU level versus higher levels. As an example, if the element at index 0 (CPU power level) in the pwr_domain_state array indicates a power down state, special hardware logic may be programmed in order to keep track of the residency statistics. For higher levels (array indices > 0), the residency statistics could be tracked in software using PMF. If ENABLE_PMF is set, the default implementation will use PMF to capture timestamps.

Function : plat_psci_stat_accounting_stop() [optional]

Argument : const psci_power_state_t *
Return   : void

This is an optional hook that platforms can implement for residency statistics accounting after exiting from a low power state. The pwr_domain_state field of state_info (first argument) can be inspected if stat accounting is done differently at CPU level versus higher levels. As an example, if the element at index 0 (CPU power level) in the pwr_domain_state array indicates a power down state, special hardware logic may be programmed in order to keep track of the residency statistics. For higher levels (array indices > 0), the residency statistics could be tracked in software using PMF. If ENABLE_PMF is set, the default implementation will use PMF to capture timestamps.

Function : plat_psci_stat_get_residency() [optional]

Argument : unsigned int, const psci_power_state_t *, int
Return   : u_register_t

This is an optional interface that is is invoked after resuming from a low power state and provides the time spent resident in that low power state by the power domain at a particular power domain level. When a CPU wakes up from suspend, all its parent power domain levels are also woken up. The generic PSCI code invokes this function for each parent power domain that is resumed and it identified by the lvl (first argument) parameter. The state_info (second argument) describes the low power state that the power domain has resumed from. The current CPU is the first CPU in the power domain to resume from the low power state and the last_cpu_idx (third parameter) is the index of the last CPU in the power domain to suspend and may be needed to calculate the residency for that power domain.

Function : plat_get_target_pwr_state() [optional]

Argument : unsigned int, const plat_local_state_t *, unsigned int
Return   : plat_local_state_t

The PSCI generic code uses this function to let the platform participate in state coordination during a power management operation. The function is passed a pointer to an array of platform specific local power state states (second argument) which contains the requested power state for each CPU at a particular power domain level lvl (first argument) within the power domain. The function is expected to traverse this array of upto ncpus (third argument) and return a coordinated target power state by the comparing all the requested power states. The target power state should not be deeper than any of the requested power states.

A weak definition of this API is provided by default wherein it assumes that the platform assigns a local state value in order of increasing depth of the power state i.e. for two power states X & Y, if X < Y then X represents a shallower power state than Y. As a result, the coordinated target local power state for a power domain will be the minimum of the requested local power state values.

Function : plat_get_power_domain_tree_desc() [mandatory]

Argument : void
Return   : const unsigned char *

This function returns a pointer to the byte array containing the power domain topology tree description. The format and method to construct this array are described in Power Domain Topology Design. The BL31 PSCI initilization code requires this array to be described by the platform, either statically or dynamically, to initialize the power domain topology tree. In case the array is populated dynamically, then plat_core_pos_by_mpidr() and plat_my_core_pos() should also be implemented suitably so that the topology tree description matches the CPU indices returned by these APIs. These APIs together form the platform interface for the PSCI topology framework.

Function : plat_setup_psci_ops() [mandatory]

Argument : uintptr_t, const plat_psci_ops **
Return   : int

This function may execute with the MMU and data caches enabled if the platform port does the necessary initializations in bl31_plat_arch_setup(). It is only called by the primary CPU.

This function is called by PSCI initialization code. Its purpose is to let the platform layer know about the warm boot entrypoint through the sec_entrypoint (first argument) and to export handler routines for platform-specific psci power management actions by populating the passed pointer with a pointer to BL31's private plat_psci_ops structure.

A description of each member of this structure is given below. Please refer to the ARM FVP specific implementation of these handlers in plat/arm/board/fvp/fvp_pm.c as an example. For each PSCI function that the platform wants to support, the associated operation or operations in this structure must be provided and implemented (Refer section 4 of Firmware Design for the PSCI API supported in Trusted Firmware). To disable a PSCI function in a platform port, the operation should be removed from this structure instead of providing an empty implementation.

plat_psci_ops.cpu_standby()

Perform the platform-specific actions to enter the standby state for a cpu indicated by the passed argument. This provides a fast path for CPU standby wherein overheads of PSCI state management and lock acquistion is avoided. For this handler to be invoked by the PSCI CPU_SUSPEND API implementation, the suspend state type specified in the power-state parameter should be STANDBY and the target power domain level specified should be the CPU. The handler should put the CPU into a low power retention state (usually by issuing a wfi instruction) and ensure that it can be woken up from that state by a normal interrupt. The generic code expects the handler to succeed.

plat_psci_ops.pwr_domain_on()

Perform the platform specific actions to power on a CPU, specified by the MPIDR (first argument). The generic code expects the platform to return PSCI_E_SUCCESS on success or PSCI_E_INTERN_FAIL for any failure.

plat_psci_ops.pwr_domain_off()

Perform the platform specific actions to prepare to power off the calling CPU and its higher parent power domain levels as indicated by the target_state (first argument). It is called by the PSCI CPU_OFF API implementation.

The target_state encodes the platform coordinated target local power states for the CPU power domain and its parent power domain levels. The handler needs to perform power management operation corresponding to the local state at each power level.

For this handler, the local power state for the CPU power domain will be a power down state where as it could be either power down, retention or run state for the higher power domain levels depending on the result of state coordination. The generic code expects the handler to succeed.

plat_psci_ops.pwr_domain_suspend()

Perform the platform specific actions to prepare to suspend the calling CPU and its higher parent power domain levels as indicated by the target_state (first argument). It is called by the PSCI CPU_SUSPEND API implementation.

The target_state has a similar meaning as described in the pwr_domain_off() operation. It encodes the platform coordinated target local power states for the CPU power domain and its parent power domain levels. The handler needs to perform power management operation corresponding to the local state at each power level. The generic code expects the handler to succeed.

The difference between turning a power domain off versus suspending it is that in the former case, the power domain is expected to re-initialize its state when it is next powered on (see pwr_domain_on_finish()). In the latter case, the power domain is expected to save enough state so that it can resume execution by restoring this state when its powered on (see pwr_domain_suspend_finish()).

plat_psci_ops.pwr_domain_pwr_down_wfi()

This is an optional function and, if implemented, is expected to perform platform specific actions including the wfi invocation which allows the CPU to powerdown. Since this function is invoked outside the PSCI locks, the actions performed in this hook must be local to the CPU or the platform must ensure that races between multiple CPUs cannot occur.

The target_state has a similar meaning as described in the pwr_domain_off() operation and it encodes the platform coordinated target local power states for the CPU power domain and its parent power domain levels. This function must not return back to the caller.

If this function is not implemented by the platform, PSCI generic implementation invokes psci_power_down_wfi() for power down.

plat_psci_ops.pwr_domain_on_finish()

This function is called by the PSCI implementation after the calling CPU is powered on and released from reset in response to an earlier PSCI CPU_ON call. It performs the platform-specific setup required to initialize enough state for this CPU to enter the normal world and also provide secure runtime firmware services.

The target_state (first argument) is the prior state of the power domains immediately before the CPU was turned on. It indicates which power domains above the CPU might require initialization due to having previously been in low power states. The generic code expects the handler to succeed.

plat_psci_ops.pwr_domain_suspend_finish()

This function is called by the PSCI implementation after the calling CPU is powered on and released from reset in response to an asynchronous wakeup event, for example a timer interrupt that was programmed by the CPU during the CPU_SUSPEND call or SYSTEM_SUSPEND call. It performs the platform-specific setup required to restore the saved state for this CPU to resume execution in the normal world and also provide secure runtime firmware services.

The target_state (first argument) has a similar meaning as described in the pwr_domain_on_finish() operation. The generic code expects the platform to succeed.

plat_psci_ops.system_off()

This function is called by PSCI implementation in response to a SYSTEM_OFF call. It performs the platform-specific system poweroff sequence after notifying the Secure Payload Dispatcher.

plat_psci_ops.system_reset()

This function is called by PSCI implementation in response to a SYSTEM_RESET call. It performs the platform-specific system reset sequence after notifying the Secure Payload Dispatcher.

plat_psci_ops.validate_power_state()

This function is called by the PSCI implementation during the CPU_SUSPEND call to validate the power_state parameter of the PSCI API and if valid, populate it in req_state (second argument) array as power domain level specific local states. If the power_state is invalid, the platform must return PSCI_E_INVALID_PARAMS as error, which is propagated back to the normal world PSCI client.

plat_psci_ops.validate_ns_entrypoint()

This function is called by the PSCI implementation during the CPU_SUSPEND, SYSTEM_SUSPEND and CPU_ON calls to validate the non-secure entry_point parameter passed by the normal world. If the entry_point is invalid, the platform must return PSCI_E_INVALID_ADDRESS as error, which is propagated back to the normal world PSCI client.

plat_psci_ops.get_sys_suspend_power_state()

This function is called by the PSCI implementation during the SYSTEM_SUSPEND call to get the req_state parameter from platform which encodes the power domain level specific local states to suspend to system affinity level. The req_state will be utilized to do the PSCI state coordination and pwr_domain_suspend() will be invoked with the coordinated target state to enter system suspend.

plat_psci_ops.get_pwr_lvl_state_idx()

This is an optional function and, if implemented, is invoked by the PSCI implementation to convert the local_state (first argument) at a specified pwr_lvl (second argument) to an index between 0 and PLAT_MAX_PWR_LVL_STATES - 1. This function is only needed if the platform supports more than two local power states at each power domain level, that is PLAT_MAX_PWR_LVL_STATES is greater than 2, and needs to account for these local power states.

plat_psci_ops.translate_power_state_by_mpidr()

This is an optional function and, if implemented, verifies the power_state (second argument) parameter of the PSCI API corresponding to a target power domain. The target power domain is identified by using both MPIDR (first argument) and the power domain level encoded in power_state. The power domain level specific local states are to be extracted from power_state and be populated in the output_state (third argument) array. The functionality is similar to the validate_power_state function described above and is envisaged to be used in case the validity of power_state depend on the targeted power domain. If the power_state is invalid for the targeted power domain, the platform must return PSCI_E_INVALID_PARAMS as error. If this function is not implemented, then the generic implementation relies on validate_power_state function to translate the power_state.

This function can also be used in case the platform wants to support local power state encoding for power_state parameter of PSCI_STAT_COUNT/RESIDENCY APIs as described in Section 5.18 of PSCI.

plat_psci_ops.get_node_hw_state()

This is an optional function. If implemented this function is intended to return the power state of a node (identified by the first parameter, the MPIDR) in the power domain topology (identified by the second parameter, power_level), as retrieved from a power controller or equivalent component on the platform. Upon successful completion, the implementation must map and return the final status among HW_ON, HW_OFF or HW_STANDBY. Upon encountering failures, it must return either PSCI_E_INVALID_PARAMS or PSCI_E_NOT_SUPPORTED as appropriate.

Implementations are not expected to handle power_levels greater than PLAT_MAX_PWR_LVL.

3.6 Interrupt Management framework (in BL31)

BL31 implements an Interrupt Management Framework (IMF) to manage interrupts generated in either security state and targeted to EL1 or EL2 in the non-secure state or EL3/S-EL1 in the secure state. The design of this framework is described in the IMF Design Guide

A platform should export the following APIs to support the IMF. The following text briefly describes each api and its implementation in ARM standard platforms. The API implementation depends upon the type of interrupt controller present in the platform. ARM standard platform layer supports both ARM Generic Interrupt Controller version 2.0 (GICv2) and 3.0 (GICv3). Juno builds the ARM Standard layer to use GICv2 and the FVP can be configured to use either GICv2 or GICv3 depending on the build flag FVP_USE_GIC_DRIVER (See FVP platform specific build options in User Guide for more details).

Function : plat_interrupt_type_to_line() [mandatory]

Argument : uint32_t, uint32_t
Return   : uint32_t

The ARM processor signals an interrupt exception either through the IRQ or FIQ interrupt line. The specific line that is signaled depends on how the interrupt controller (IC) reports different interrupt types from an execution context in either security state. The IMF uses this API to determine which interrupt line the platform IC uses to signal each type of interrupt supported by the framework from a given security state. This API must be invoked at EL3.

The first parameter will be one of the INTR_TYPE_* values (see IMF Design Guide) indicating the target type of the interrupt, the second parameter is the security state of the originating execution context. The return result is the bit position in the SCR_EL3 register of the respective interrupt trap: IRQ=1, FIQ=2.

In the case of ARM standard platforms using GICv2, S-EL1 interrupts are configured as FIQs and Non-secure interrupts as IRQs from either security state.

In the case of ARM standard platforms using GICv3, the interrupt line to be configured depends on the security state of the execution context when the interrupt is signalled and are as follows:

• The S-EL1 interrupts are signaled as IRQ in S-EL0/1 context and as FIQ in NS-EL0/1/2 context.
• The Non secure interrupts are signaled as FIQ in S-EL0/1 context and as IRQ in the NS-EL0/1/2 context.
• The EL3 interrupts are signaled as FIQ in both S-EL0/1 and NS-EL0/1/2 context.

Function : plat_ic_get_pending_interrupt_type() [mandatory]

Argument : void
Return   : uint32_t

This API returns the type of the highest priority pending interrupt at the platform IC. The IMF uses the interrupt type to retrieve the corresponding handler function. INTR_TYPE_INVAL is returned when there is no interrupt pending. The valid interrupt types that can be returned are INTR_TYPE_EL3, INTR_TYPE_S_EL1 and INTR_TYPE_NS. This API must be invoked at EL3.

In the case of ARM standard platforms using GICv2, the Highest Priority Pending Interrupt Register (GICC_HPPIR) is read to determine the id of the pending interrupt. The type of interrupt depends upon the id value as follows.

1. id < 1022 is reported as a S-EL1 interrupt
2. id = 1022 is reported as a Non-secure interrupt.
3. id = 1023 is reported as an invalid interrupt type.

In the case of ARM standard platforms using GICv3, the system register ICC_HPPIR0_EL1, Highest Priority Pending group 0 Interrupt Register, is read to determine the id of the pending interrupt. The type of interrupt depends upon the id value as follows.

1. id = PENDING_G1S_INTID (1020) is reported as a S-EL1 interrupt
2. id = PENDING_G1NS_INTID (1021) is reported as a Non-secure interrupt.
3. id = GIC_SPURIOUS_INTERRUPT (1023) is reported as an invalid interrupt type.
4. All other interrupt id's are reported as EL3 interrupt.

Function : plat_ic_get_pending_interrupt_id() [mandatory]

Argument : void
Return   : uint32_t

This API returns the id of the highest priority pending interrupt at the platform IC. INTR_ID_UNAVAILABLE is returned when there is no interrupt pending.

In the case of ARM standard platforms using GICv2, the Highest Priority Pending Interrupt Register (GICC_HPPIR) is read to determine the id of the pending interrupt. The id that is returned by API depends upon the value of the id read from the interrupt controller as follows.

1. id < 1022. id is returned as is.
2. id = 1022. The Aliased Highest Priority Pending Interrupt Register (GICC_AHPPIR) is read to determine the id of the non-secure interrupt. This id is returned by the API.
3. id = 1023. INTR_ID_UNAVAILABLE is returned.

In the case of ARM standard platforms using GICv3, if the API is invoked from EL3, the system register ICC_HPPIR0_EL1, Highest Priority Pending Interrupt group 0 Register, is read to determine the id of the pending interrupt. The id that is returned by API depends upon the value of the id read from the interrupt controller as follows.

1. id < PENDING_G1S_INTID (1020). id is returned as is.
2. id = PENDING_G1S_INTID (1020) or PENDING_G1NS_INTID (1021). The system register ICC_HPPIR1_EL1, Highest Priority Pending Interrupt group 1 Register is read to determine the id of the group 1 interrupt. This id is returned by the API as long as it is a valid interrupt id
3. If the id is any of the special interrupt identifiers, INTR_ID_UNAVAILABLE is returned.

When the API invoked from S-EL1 for GICv3 systems, the id read from system register ICC_HPPIR1_EL1, Highest Priority Pending group 1 Interrupt Register, is returned if is not equal to GIC_SPURIOUS_INTERRUPT (1023) else INTR_ID_UNAVAILABLE is returned.

Function : plat_ic_acknowledge_interrupt() [mandatory]

Argument : void
Return   : uint32_t

This API is used by the CPU to indicate to the platform IC that processing of the highest pending interrupt has begun. It should return the id of the interrupt which is being processed.

This function in ARM standard platforms using GICv2, reads the Interrupt Acknowledge Register (GICC_IAR). This changes the state of the highest priority pending interrupt from pending to active in the interrupt controller. It returns the value read from the GICC_IAR. This value is the id of the interrupt whose state has been changed.

In the case of ARM standard platforms using GICv3, if the API is invoked from EL3, the function reads the system register ICC_IAR0_EL1, Interrupt Acknowledge Register group 0. If the API is invoked from S-EL1, the function reads the system register ICC_IAR1_EL1, Interrupt Acknowledge Register group 1. The read changes the state of the highest pending interrupt from pending to active in the interrupt controller. The value read is returned and is the id of the interrupt whose state has been changed.

The TSP uses this API to start processing of the secure physical timer interrupt.

Function : plat_ic_end_of_interrupt() [mandatory]

Argument : uint32_t
Return   : void

This API is used by the CPU to indicate to the platform IC that processing of the interrupt corresponding to the id (passed as the parameter) has finished. The id should be the same as the id returned by the plat_ic_acknowledge_interrupt() API.

ARM standard platforms write the id to the End of Interrupt Register (GICC_EOIR) in case of GICv2, and to ICC_EOIR0_EL1 or ICC_EOIR1_EL1 system register in case of GICv3 depending on where the API is invoked from, EL3 or S-EL1. This deactivates the corresponding interrupt in the interrupt controller.

The TSP uses this API to finish processing of the secure physical timer interrupt.

Function : plat_ic_get_interrupt_type() [mandatory]

Argument : uint32_t
Return   : uint32_t

This API returns the type of the interrupt id passed as the parameter. INTR_TYPE_INVAL is returned if the id is invalid. If the id is valid, a valid interrupt type (one of INTR_TYPE_EL3, INTR_TYPE_S_EL1 and INTR_TYPE_NS) is returned depending upon how the interrupt has been configured by the platform IC. This API must be invoked at EL3.

ARM standard platforms using GICv2 configures S-EL1 interrupts as Group0 interrupts and Non-secure interrupts as Group1 interrupts. It reads the group value corresponding to the interrupt id from the relevant Interrupt Group Register (GICD_IGROUPRn). It uses the group value to determine the type of interrupt.

In the case of ARM standard platforms using GICv3, both the Interrupt Group Register (GICD_IGROUPRn) and Interrupt Group Modifier Register (GICD_IGRPMODRn) is read to figure out whether the interrupt is configured as Group 0 secure interrupt, Group 1 secure interrupt or Group 1 NS interrupt.

3.7 Crash Reporting mechanism (in BL31)

BL31 implements a crash reporting mechanism which prints the various registers of the CPU to enable quick crash analysis and debugging. It requires that a console is designated as the crash console by the platform which will be used to print the register dump.

The following functions must be implemented by the platform if it wants crash reporting mechanism in BL31. The functions are implemented in assembly so that they can be invoked without a C Runtime stack.

Function : plat_crash_console_init

Argument : void
Return   : int

This API is used by the crash reporting mechanism to initialize the crash console. It must only use the general purpose registers x0 to x4 to do the initialization and returns 1 on success.

Function : plat_crash_console_putc

Argument : int
Return   : int

This API is used by the crash reporting mechanism to print a character on the designated crash console. It must only use general purpose registers x1 and x2 to do its work. The parameter and the return value are in general purpose register x0.

4. Build flags

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• ENABLE_PLAT_COMPAT All the platforms ports conforming to this API specification should define the build flag ENABLE_PLAT_COMPAT to 0 as the compatibility layer should be disabled. For more details on compatibility layer, refer Migration Guide.

There are some build flags which can be defined by the platform to control inclusion or exclusion of certain BL stages from the FIP image. These flags need to be defined in the platform makefile which will get included by the build system.

• NEED_BL33 By default, this flag is defined yes by the build system and BL33 build option should be supplied as a build option. The platform has the option of excluding the BL33 image in the fip image by defining this flag to no. If any of the options EL3_PAYLOAD_BASE or PRELOADED_BL33_BASE are used, this flag will be set to no automatically.

5. C Library

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To avoid subtle toolchain behavioral dependencies, the header files provided by the compiler are not used. The software is built with the -nostdinc flag to ensure no headers are included from the toolchain inadvertently. Instead the required headers are included in the ARM Trusted Firmware source tree. The library only contains those C library definitions required by the local implementation. If more functionality is required, the needed library functions will need to be added to the local implementation.

Versions of FreeBSD headers can be found in include/lib/stdlib. Some of these headers have been cut down in order to simplify the implementation. In order to minimize changes to the header files, the FreeBSD layout has been maintained. The generic C library definitions can be found in include/lib/stdlib with more system and machine specific declarations in include/lib/stdlib/sys and include/lib/stdlib/machine.

The local C library implementations can be found in lib/stdlib. In order to extend the C library these files may need to be modified. It is recommended to use a release version of FreeBSD as a starting point.

The C library header files in the FreeBSD source tree are located in the include and sys/sys directories. FreeBSD machine specific definitions can be found in the sys/<machine-type> directories. These files define things like 'the size of a pointer' and 'the range of an integer'. Since an AArch64 port for FreeBSD does not yet exist, the machine specific definitions are based on existing machine types with similar properties (for example SPARC64).

Where possible, C library function implementations were taken from FreeBSD as found in the lib/libc directory.

A copy of the FreeBSD sources can be downloaded with git.

git clone git://github.com/freebsd/freebsd.git -b origin/release/9.2.0

6. Storage abstraction layer

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In order to improve platform independence and portability an storage abstraction layer is used to load data from non-volatile platform storage.

Each platform should register devices and their drivers via the Storage layer. These drivers then need to be initialized by bootloader phases as required in their respective blx_platform_setup() functions. Currently storage access is only required by BL1 and BL2 phases. The load_image() function uses the storage layer to access non-volatile platform storage.

It is mandatory to implement at least one storage driver. For the ARM development platforms the Firmware Image Package (FIP) driver is provided as the default means to load data from storage (see the "Firmware Image Package" section in the User Guide). The storage layer is described in the header file include/drivers/io/io_storage.h. The implementation of the common library is in drivers/io/io_storage.c and the driver files are located in drivers/io/.

Each IO driver must provide io_dev_* structures, as described in drivers/io/io_driver.h. These are returned via a mandatory registration function that is called on platform initialization. The semi-hosting driver implementation in io_semihosting.c can be used as an example.

The Storage layer provides mechanisms to initialize storage devices before IO operations are called. The basic operations supported by the layer include open(), close(), read(), write(), size() and seek(). Drivers do not have to implement all operations, but each platform must provide at least one driver for a device capable of supporting generic operations such as loading a bootloader image.

The current implementation only allows for known images to be loaded by the firmware. These images are specified by using their identifiers, as defined in [include/plat/common/platform_def.h] (or a separate header file included from there). The platform layer (plat_get_image_source()) then returns a reference to a device and a driver-specific spec which will be understood by the driver to allow access to the image data.

The layer is designed in such a way that is it possible to chain drivers with other drivers. For example, file-system drivers may be implemented on top of physical block devices, both represented by IO devices with corresponding drivers. In such a case, the file-system "binding" with the block device may be deferred until the file-system device is initialised.

The abstraction currently depends on structures being statically allocated by the drivers and callers, as the system does not yet provide a means of dynamically allocating memory. This may also have the affect of limiting the amount of open resources per driver.

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Copyright (c) 2013-2016, ARM Limited and Contributors. All rights reserved.